Observation of low field magnetoresistance in the layered manganite Sr1.6Sm1.4Mn2O7

The structural, transport, and magnetic properties of the naturally layered manganese oxide, Sr1.6Sm1.4Mn2O7 (Sm-327), which consists of two [MnO2] bi -layers intertwined with a rock-salt type layer of [(Sr,Sm)(2)O-2] have bee n investigated. Both a sharp metal-insulator (M-I) transition and an antife rromagnetic transition were found to occur simultaneously at about 118 K. E ven in the absence of ferromagnetic ordering the resistance is suppressed r emarkably upon applying a magnetic field. These results suggest that the M- I transition and colossal magnetoresistance behavior observed in Sm-327 are not driven mainly by the double exchange mechanism but ascribed rather to the canted antiferromagnetic spin configurations of [MnO2] bi-layers, which eventually leads to the field-induced ferromagnetic ordering. (C) 1999 Els evier Science Ltd. All rights reserved.